The present invention relates to a hydraulic control valve.
The limits to the utilization of directly operated hydraulic valves are essentially dictated by the ratio of flow forces to actuating forces. If the flow force can be reduced, the utilization limits can be extended or the actuating force reduced. In respect of the cause, amount and direction of action of such flow forces at control edges of hydraulic valves, reference is made to relevant literature, for example the information that can be gained from the textbook by J. F. Blackburn, G. Reethof, J. L. Shaerer: Fluid Power Control I, II, III, Krausskopfverlag, Mainz 1962. Various possible ways of reducing such flow forces have also already been described, although as a rule such known methods can be employed only for inlet or outlet control edges, while at the same time giving rise to a heavy static pressure loss and generally entail considerable expense. An additional factor is that flow force compensation at an outlet control edge is incomparably more difficult to achieve than at an inlet control edge.
From the records of the 9th Aachen Fluid Technology Colloquium 1990, in the contribution "Flow Force Compensation in Hydraulic Slide Valves" by H. J. Feigel, Pages 79 to 97, a congeneric hydraulic control valve comprising a device for flow force compensation at an outlet control edge is known. The control valve is here in the form of an electromagnetically operable four-way control valve having four pairs of control edges, each outlet control edge having a flow force compensation device in which a spool sleeve receiving the control spool has, in the region of an outlet control edge, a deflecting annular groove disposed in the sleeve. In order here to avoid expensive internal machining, the spool sleeve has a configuration in which a middle sleeve is provided at each of its two outer ends with an additional attached sleeve. In this way the outlet control edge on the sleeve can be produced relatively simply and with accurate dimensions by facing. Furthermore, the deflecting annular groove is formed by the attached sleeve fitted, which has a larger diameter. It is now a disadvantage of this solution that in order to avoid internal machining of the outlet control edge great expense has to be incurred here to achieve flow force compensation. Thus, this valve works with a three-part spool sleeve arranged, with different outside diameters, in the casing. This requires accurate machining of the casing to avoid jamming of the spool with the multi-part spool sleeve construction. Moreover, axially extending pins are disposed on the middle sleeve, starting from the outlet control edge, so that simple production of the outlet control edge, for example by turning, is not possible. In addition, with this configuration it is hard to achieve desired flow geometries at the control edges. Furthermore, the multipart sleeve construction entails increased expense for sealing. The manufacture and assembly of the control valve also become more difficult.
In addition, from EP 0 030 336 B1 a pressure-reducing valve is known, which is constructed in the style of an insertable valve and has flow force compensation. The flow force compensation device is here constructed for an inlet control edge, the control spool disposed in a sleeve being provided, in a duct region through which the pressure medium flows, with a piston collar which has conical bevels and which generates compensating impulse forces. No compensation for flow forces at an outlet control edge is provided here.